Generally, optical disks use easily fusible or sublimatable metal or pigment as the information recording material Information is recorded on these recording materials by irradiating the recording material with a laser light to form pits. The information recorded on these different types of recording materials can be reproduced, but it cannot be erased. More specifically, it is not possible to record information on a track of a disk having information previously recorded on that same track, although it is possible to record information on other tracks of the disk which have no information recorded thereon.
On the other hand, optical disks formed of an amorphous or of a photomagnetic recording material Which have information recorded thereon by, for example phase change Kerr effect or the like, have an advantage in that not only is it possible to reproduce information previously recorded on the disk, but it is also possible to erase information recorded on the disk for rewriting new information on that disk.
As described above, optical disks used for optically recording/reproducing information by irradiating a laser light and the like on the disk can be classified into three different types. More specifically, optical disks can be classified into a first disk of the read-only type, a second disk of the nonerasable read/write type, and a third disk of the erasable read/write type.
In recording or reproducing information onto or from a disk, the optimum intensity of the laser light used for recording or reproducing varies according to the type of disk. Further, the reflectivity of a disk also varies according to the type of disk. Accordingly, it is necessary to adjust the AGC corresponding to the particular type of disk.
In previous conventional systems, a plurality of data or information representing the type of disk, the optimum light intensity, the reflectivity of the disk and the like, have been recorded on a predetermined position of the disk in advance, so that this data can be read before a recording/reproducing operation is initiated. This data is used to establish respective operating conditions of the system corresponding to the data.
According to the aforementioned conventional system, data for establishing different operating conditions of the system must be separately recorded on each disk. Data relating to the optimum light intensity for use in recording and erasing operations have not been recorded on disks of the read-only type, since this data has no use in read-only type disks. Therefore, data relating to the optimum light intensity for use in recording and erasing operations has only been recorded on the erasable read/write type of disks. As discussed above, the operating conditions of a disk varies according to the type of disk. Heretofore, this has been a barrier in providing a single recording/reproducing unit or disk drive which can record/reproduce information from/onto different types of disks.